mechanism of labor_ppt.pptx a reference for Maternal and Child

Mechanism Of Labor

1. MECHANISM OF LABOUR

2. Series of events that take place in the genital organs in an effort to expel the viable products of conception (fetus, placenta and the membranes) out of the womb through the vagina into the outer world is called labour . LABOUR

3. The physiological and anatomical principles involved in normal and abnormal labor is best summarized using the ‘ 3 Ps ’, which are the powers, the passages and the passenger. When 3Ps are favorable, normal labour is likely to ensue, resulting in an unassisted or spontaneous vaginal birth. NORMAL LABOUR

4. In 1996, the World Health Organization (WHO) defined normal labour as follow: It should be spontaneous in onset. The infant is born spontaneously in the vertex position between at term through the birth canal. After birth, mother and infant are in good condition. WHO CRITERIA OF NORMAL LABOUR

5. When any of the 3Ps are unfavorable, OR any deviation from the criteria of normal labour then it is termed as abnormal , resulting in the need for intervention and with that, an increased risk of morbidity or mortality. ABNORMAL LABOUR

6. The first important step is to recognize when labor has started. The Naegele’s formula is simple arithmetic method for calculating the EDD (estimated date of delivery) based on the LMP (Last menstrual period.) Key points are Menstrual cycle of 28 days and gestational period of 280 days. N AEGELE'S FORMULA

7. There are two formulas: First formula: LMP date - 3 months from the LMP + 7 days in LMP + 1 year Example: LMP date: September 28, 2018- 3 months = June 28, 2018+7 days = July 5, 2018+1 year = July 5, 2019 N AEGELE'S FORMULA

8. Second formula: LMP date + 7 days in LMP + 9 months Example: LMP date: September 28, 2018+7 days = October 5, 2018+ 9 months = July 5, 2019 NAEGELE'S FORMULA

9. The onset of labour occurs when the factors that inhibit contractions and maintain a closed cervix diminish and are overtaken by the actions of factors that do the opposite. These includes; Hormonal Factors Mechanical Factors CAUSES OF ONSET OF LABOUR

10. Stretching effect on the myometrium by the growing fetus and liquor amnii. Uterine stretch increases gap junction proteins, receptors for oxytocin and specific contraction associated proteins. MECHANICAL FACTORS

11. Estrogen: During pregnancy, most of the estrogens are present in a binding form. During the last trimester, more free estrogen appears increasing the excitability of the myometrium and prostaglandins synthesis. Progesterone : Before labor, there is a drop in progesterone synthesis leading to the predominance of the excitatory action of estrogens. Oxytocin: Release from the posterior pituitary. It increases the strength of uterine contractions. The Ferguson reflex is a neuroendocrine reflex in which the fetal distension of the cervix stimulates a series of neuroendocrine responses, leading to oxytocin production Prostaglandins: E2 and F2α are powerful stimulators of uterine muscle activity. It is synthesized by the chorion and the decidua is enhanced, leading to an increase in calcium influx into the myometrial cells. HORMONAL FACTORS

12. This change in the hormones also increases gap junction formation between individual myometrial cells, which is necessary for coordinated uterine activity. The production of corticotrophin-releasing hormone (CRH) by the placenta increases in concentration towards term and potentiates the action of prostaglandins and oxytocin on myometrial contractility. The fetal pituitary secretes oxytocin and the fetal adrenal gland produces cortisol , which stimulates the conversion of progesterone to estrogen. HORMONAL FACTORS

13. Labor is then divided into three stages: First stage: It begins with diagnosis of the onset of labor and is complete when full cervical dilatation has been reached. Second stage: It begins with full cervical dilatation and ends with birth of the baby. Third stage: It begins with birth of the baby and ends with complete delivery of the placenta and membranes. STAGES OF LABOUR

14. The onset of labor is defined by strong, regular, and painful contractions that cause the cervix to change. Labor is diagnosed with at least two vaginal exams showing cervical progress. When a woman feels contraction- like pains, a doctor confirms labor through a vaginal exam showing the cervix thinning and dilating. DIAGNOSIS OF LABOUR

15. Retraction is a phenomenon of the uterus in labour in which the muscle fibres are permanently shortened .

16. Time interval between the diagnosis of labour to full dilatation of the cervix (10 cm). Two phases: Latent phase: (0 to 3-4cm cervical dilatation) During this time, the cervix becomes ‘fully effaced’. It usually lasts between 3 and 8 hours. Active phase: (4 to 10cm cervical dilatation). It usually lasting between 2 and 6 hours. 1 st STAGE

17. Dilatation s Effacement of cervix

18. The time from full dilatation of the cervix to delivery of the fetus or fetuses. Two phases: Passive phase describes the time between full dilatation and the onset of involuntary expulsive contractions. There is no maternal urge to push and the fetal head is still relatively high in the pelvis. Active phase is distinguished by maternal bearing down efforts and ends with delivery of the baby. Average duration is 2 hours. 2 nd STAGE

19. It begins after expulsion of the fetus and ends with expulsion of the placenta and membranes (after- births). Its average duration is about 15 minutes in both primigravidae and multiparae. A third stage lasting more than 30 minutes is defined as abnormal . 3 rd STAGE

20. There is no perfect labor length for all women, but problems arise if labor is too fast or too slow. Morale drops after 6 hours in labor and worsens after 12 hours. Longer labor increases the risk of fetal hypoxia and the need for operative delivery. Prolonged labor is over 12 hours for first- time mothers and over 8 hours for mothers who have given birth before. Precipitous labor is when the baby is born within 3 hours of regular contractions starting. DURATION OF LABOUR

21. This refers to the series of changes in position and attitude that the fetus undergoes during its passage through the birth canal. MECHANISM OF LABOUR

22. Presentation: It refers to the part of the fetus’s body that enters the pelvic inlet. Lie: Relation between the long axis of the fetus to the long axis of the uterus. Longitudinal Oblique Transverse MECHANISM OF LABOUR

23. Position: refers to presenting part of the fetus in relation to pubic symphysis of mother. MECHANISM OF LABOUR Attitude: Degree of flexion and extension at upper cervical spines.

24. Engagement: Engagement occurs when the widest part of the head passes through the pelvic inlet. For primigravidae , this happens by 37 weeks of pregnancy. Engagement is checked by feeling the fetal head through the abdomen. If more than two-fifths of the head can be felt, it is not yet engaged. The fetal head enters the pelvis in a transverse position, using the widest pelvic diameter.

25. Descent: Here the baby descends from pelvic inlet towards the pelvic floor. It occurs due to uterine contractions (1 st and first phase of 2 nd stage) and abdominal muscle contraction (second phase of 2 nd stage). Flexion: The fetal head isn’t always fully flexed when entering the pelvis. As it descends into the narrower midpelvis, it flexes. This movement helps reduce the head’s presenting diameter.

26. Internal Rotation: If the head is well flexed, the occiput leads and rotates anteriorly i.e. in OA position, aligning with the pelvic outlet’s widest diameter. If the fetus starts to descend in the OP position, it can rotate to the OA position, which may lengthen labor. And if the OP position persists, the baby may be born “face to pubes ,” causing head extension and increasing the diameter presented to the pelvic outlet . This can lead to obstructed labor, requiring instrumental delivery or a C- section.

27. Extension: After internal rotation, the occiput is under the pubic symphysis, and the bregma is near the sacrum. The head extends, the occiput emerges from under the pubic bone, and the vulva stretches, which is called "crowning." As the head extends more, the face and chin appear. Controlled extension reduces perineal trauma, but some tearing often occurs in first births due to resistance from the perineum.

28. Restitution & External Rotation The head slightly rotate after passing perineum to align with shoulders. This spontaneous realignment of the head with the shoulders is called restitution. The occiput have to further rotate externally to a transverse position. This is called External rotation.

29. Delivery of shoulders and fetal body: Delivery of the shoulders and body often involves gentle downward traction on the fetal head to release the anterior shoulder, followed by upward traction to guide the posterior shoulder over the perineum, facilitating the baby’s delivery onto the maternal abdomen.

30. REFERENCE